This work presents a theoretical and experimental investigation on the absorption of CO2 into piperazine (PZ) activated aqueous N-methyldiethanolamine (MDEA) solvent. A comprehensive mathematical model which is based on Higbie's penetration theory has been developed to analyze the experimental data. The model involving coupled mass transfer-reaction kinetics-chemical equilibrium incorporates the important reversible reactions in the liquid phase. The model is validated with the experimental results of steady state absorption measurements of CO2 in a 2.81 x 10(-2) in o.d. stainless steel wetted wall contactor. The rates of absorption of CO2 into this solvent have been measured over the CO2 partial pressure range of 2-14 kPa and temperature range of 298-313 K under atmospheric pressure. The absorption experiments are performed over the MDEA concentration range of 1.89-2.41 kmol m(-3) along with PZ concentrations of 0.24,0.60 and 0.95 kmol m(-3). The predicted absorption rates and enhancement factors based on the model have been found to be in good agreement with the experimental results, the average absolute deviation between the model predicted and experimental results being 6.8%. The values of the rate constants, k(23) and k(25) for the PZ-carbamate and PZ-dicarbamate formation reactions determined in this work have been found to be about 17,500 m(6) kmol(-2) s(-1) and 15,500 m(6) kmol(-2) s(-1) at 298K, respectively. Good agreement between the model predicted and experimental results validates the mathematical model developed in this work to represent CO2 mass transfer in PZ activated aqueous MDEA. (C) 2011 Elsevier B.V. All rights reserved.